1. Field of the Invention
The present invention is directed to a spectroscopically selective filter device for light which is conveyed in a film waveguide arranged on a substrate.
2. Prior Art
Filter devices for light in film waveguides are known. An article by D. C. Flanders, H. Kogelnik, R. V. Schmidt and C. V. Shank, "Grating Filters For Thin-Film Optical Waveguides" Applied Physics Letters, Vol. 24, No. 4, Feb. 15, 1974, pages 194-196, describes a grating filter for a film waveguide. In the described device, a surface relief grating is engraved on the surface of the waveguide. If a light wave passes through the waveguide beneath this grating, it is separated into a transmission component and a reflection component in a spectroscopical fashion. However, only a half-value band width of 0.2 nm of filtered light can be obtained by this device.